jacko61

I have a Baader and SvBony IR/UV cut filters. I never use the Svbony. Graeme

DHL just brought a big box and a small package. Ordered from Ian at Altair Astro late Wednesday night - certainly can't fault the turnaround. Just needs the right mounting plate - the EQ8R-pro doesn't support vixen.

At face value, the third photo looks to be closer to the correct back focus than the other two. Looking at the first one, the stars on the left of the pic all seem to be rushing away from the centre which is what we'd expect if the sensor is too close. However, the stars down the right hand side don't seem to show anywhere near as much distortion. It's possible that this is due to poor collimation but it could also be caused by some tilt somewhere in the imaging train. While the third image seems to have better back focus, the focus overall is poor. What are you using to focus? If you're using a bahtinov mask, I've read it's best to focus on a star in one of the thirds rather than a central object. Graeme

I went to that London once. It reminded me a bit of Newcastle but without the charm. Graeme.

I'd say you should be measuring from the red line. the altair site says this.. For DSLR cameras, a T-Thread adaptor of approx. 8-10mm thickness is required. Given a DSLR has 44mm from the sensor to the lens mounting plate there's no way you could have 55mm from the green line. the astro-tech says . Back focus is 55mm from the shoulder of the reducer to the image plane, the standard spacing for 35mm and DSLR camera bodies The shoulder is the edge next to the thread - again, your red line. The standard spacing for dslr cameras is 44mm from the sensor plus the 11mm T ring Graeme

And if it works then that's all that matters in the long run Graeme

Nice image. Are you using any other spacer rings with the T-adaptor? Graeme

His friend has suggested taking some images without a reducer to see if there is some fundamental issue with the mirrors. I guess he needs to know the focal plane to be able to get these 'non-reducer' images in as good focus as he possibly can. I'd suggest starting with the camera sensor 127mm from the scope 'baffle' then checking star focus with a bahtinov mask and adjusting from there. Graeme

celestron seem to think otherwise.... What are the optimum back focus distances for Celestron SCTs? | Celestron their definition is the distance from the baffle (i'e' the threaded end of the scope with the visual back removed) to the point of best focus. Whether or not we'd call it that is neither here nor there. It's the distance the OP is asking for at the end of his post.

cut and paste / copy and paste - same thing. Anyway. He asks a very specific question at the end of his post (which I have read fully a number of times BTW). He wants to know the back focus of his c8 WITHOUT a focal reducer because of some advice he's been given. That was the question I answered with a link to the celestron backfocus page. Whether what he wants to do is of any use is not for you or I to decide; we're just here to answer his question as best we can. Graeme

The very last sentence of the OP that YOU have cut and pasted says exactly what I pasted. . "does anyone know what back focus distance I need when not using a focal reducer on this scope?". I'm not sure why you can't see the word 'not' 8 words from the end. Graeme

I'd read somewhere that a simple method of figuring the back focus of a reducer was to use it to focus the sun or moon, measure that distance and halve it - should give a reasonable starting point. Graeme

Skywatching by David Levy just arrived on the mat. Looks like a very good read... Graeme

According to this review, the Antares 6.3 only needs a back focus of 49mm... f/6.3 Antares Focal Reducer for SCTs- Awesome Astrophotography However, there seems to be more discussion on the Antares on the web than all the other reducers put together. Some seem to think it's only a reducer and NOT a flattener. Some seem to think it's identical to the Celestron and probably made in the same factory (in which case how can it have a different focal length per the article above). There's some useful info on calculating a reducer's back focus at the bottom of this article.. Agena's Guide to Focal Reducers (agenaastro.com) Graeme

The OPS question... "does anyone know what back focus distance I need when not using a focal reducer on this scope?" Graeme

google is your friend.. What are the optimum back focus distances for Celestron SCTs? | Celestron so 127mm Graeme

Rother Valley Optics own brand 12v Dew Heaters are very good. Come with both RCA and 5.5x2.1mm plugs and their own voltage controller. RVO Heater Bands With Integrated Controller - Rother Valley Optics Ltd Graeme

oh - icing on the cake... All my Bodes subs from last night have dark spots in the stars so DSS won't stack them. I must have had mirror flop between focusing on Polaris (with a bhatinov) and slewing to M81 Graeme

I've cleared all the SYNC points in EQMOD. Hopefully we'll get a clear night again soon so I can do so more sluething. Graeme

Not sure how it could be a date or time thing. they are both picked up from the laptop. The slews I was platesolving have all been very close to start with. targetting the moon was several degrees away. Very odd. Maybe stellarium itself was wrong 😮 Graeme. edit. What surprised me was the fact that subsequent slews right across the sky were all very accurate - capella, M90, M3 etc but slewing back to the moon again was off by the same amount.

ADM do a tool to help with their knobs. Don't know if they're the same size as the EQ6 but you could maybe fabricate something similar. ADM Rosette Knob Hand Tool | First Light Optics Graeme

I had a bit of a breakthrough moment last night when I finally got platesolving working under APT. Slewed to various objects in Stellarium then platesolved them pretty quickly in APT - wonder why it's taken me so long to get round to it! Anyway, after 90 minutes of adding data to my M81 folder I thought I'd have another play with the GOTO's in stellarium and practice the platesolves. After a handful, Goto's were very nearly landing right on the spot BUT around 1:30am I thought I'd take a look at the moon. Pointed to it in Stellarium, clicked current object then slew and watched as the mount failed to point within 5 degrees of the moon. It ended up pointing much further west and lower in the sky. Odd. A subsequent click on Capella brought that star right into the centre of the frame. Targetting the moon once again brought the scope pointing further west - looked like exactly the same spot as before. My coordinates in Stellarium match those in EQMOD and the time is picked up from my laptop. Anyone else see this sort of behaviour using stellarium? Graeme

I have the celestron 50mm T adapter behind the 6.3 reducer. Then the 16.5mm zwo m42/m48 extension, then the 21mm Zwo filter drawer, finally the camera with it's 11mm m42 extension (this plus the 6.5mm from the front of the camera to the sensor makes up 105mm). The only problem with this set up is that the filter drawer is M48 at the scope end, the 16.5 is M42 / M48 and the celestron T extension is m42 so the setup needs three m42/m48 adapter rings - 2 at the 16.5mm m48 end and one at the 16.5mm M42 end (where the filter drawer screws on). My C8 is on a Losmandy plate for the mount. Opposite that I have an ADM mini dovetail bar and rings for the 60mm guidescope. ADM Mini Dovetail & Guidescope Rings C8 Kit | First Light Optics - a bit pricey but that's astrophotography ! There's also a couple of extra brackets for a RACI and a normal finderscope but I need to move those as they interfere with the EQ8Rpro saddle. Graeme Edit: - If you have the zwo OAG that's only 16.5mm so you'd have to use the 21mm extension tube. Figuring out where the various thread sizes are different and what adpters you'll need is the tricky bit. You might only need one between the OAG and the 21mm extension.

I've been guiding my C8 with a standard guidescope set up since I started taking astrophotography more seriously. Right from the start I've been getting good results. Guidescope is an SVBONY 60mm and I replaced the standard rings and clamps with ADM which hold the scope really solidly. Graeme

Small world - drive through Kilncadzow if I'm heading to Carluke (mostly to the tip or to take the grandkids to softplay). Originally a Northumbrian though. We've only been in Scotland 24 years and Wilsontown 6. I was advised elsewhere to give NINA a go so I've been watching a bunch of tutorials. Trouble with Wilsontown though - it's almost always cloudy so I'll have forgotten what I learned by the time I get to have another go Graeme